Author Topic: What's in inside a 4FL oil pump...  (Read 80 times)

Martin77

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What's in inside a 4FL oil pump...
« on: December 04, 2019, 10:15:32 PM »
So, after thinking about what Arrow said about uprating oil pumps for big bores, and being an inquisitive person, I decided to have a poke about inside my old 4FL pump. (I had removed it as the one way valve leaked allowing the engine to fill with oil when sat).

The stroke is checked with a dial gauge poking through the end cap, while the internal gear is turned with a spare finger, 0.25mm for minimum and 2.9mm for maximum.




So wondering if I can increase flow a bit I modded the small cam which controls the stroke..thus..
 


here's where it sits underneath the blanking plug. The small brass adjustment screw goes inside the middle of the cam and is eccentric, so when the screw is turned the cam moves in/out to fine tune the minimum stroke. It is a bit awkward to remove it.


Along with a bit of grinding on the top cam, I managed to get max stroke up to 3.4mm, or about 17-18% more flow.

What was alarming though, was when I stripped my current pump (4FL cast on the body and pulley) it had a different small cam inside giving max stroke of less than 2mm! so for the past couple of years the oil flow past 1/3 throttle would be much less than even the 125 ought to have! says a lot about fully synth oil I guess... and why the tail can is always dry inside. I wonder if they used the same pump body for 50cc versions?

Anyway, will fit the modded pump (which only pumps more past 3/4 throttle or so) and see how it goes next spring..


ybk

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Re: What's in inside a 4FL oil pump...
« Reply #1 on: December 06, 2019, 06:29:19 AM »
That's pretty neat, Arrow will be proud :) These pumps are quite bulky compared to the 3xv ones - the design has probably been improved upon significantly over the years..

Martin77

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Re: What's in inside a 4FL oil pump...
« Reply #2 on: December 06, 2019, 11:44:56 AM »
True, but it's also quite a bit better designed than the older ones, where you have to muck about with shims.. like you say, things move on!